Field of the Invention
The present disclosure relates to image forming apparatuses, such as an electrophotographic printer and an electrophotographic copying machine.
Description of the Related Art
Image forming methods used in image forming apparatuses such as a copier, regularly include an electrophotographic recording method. In such a method, a front surface of a photosensitive drum, which is an image carrying member, is uniformly charged with a charging device, an electrostatic latent image is formed with an exposing device, and the electrostatic latent image is visualized into a toner image using toner, which is a developer, with a developing apparatus. Subsequently, the toner image is transferred to a recording material, such as paper, with a transfer device, such as an intermediate transfer body, and, ultimately, is fixed with a fixing device. Meanwhile, the remaining toner that had not been transferred to the transfer material from the photosensitive drum is collected by a cleaning device abutted against the photosensitive drum.
Regarding the developing apparatus, Japanese Patent Laid-Open No. 6-43745 discloses an apparatus that employs a method in which a non-magnetic mono-component toner accommodated inside a developer container is supplied to a developing roller, which is a developer carrying member, with a supply roller, in which the thickness of the toner on the developing roller is made substantially uniform with a developing blade, which is a developer regulating member, and in which an electrostatic latent image is developed.
Furthermore, Japanese Patent Laid-Open No. 8-44206 proposes a developing apparatus that, while configured to use a non-magnetic single-component toner, does not use a supply roller. The above configuration includes a supply guide that abuts against a developing roller. The toner is conveyed and accumulated in a space formed between the developing roller and the supply guide, and the toner is supplied with a synergistic effect between the toner self-weight and the rotary force of the developing roller.
Moreover, regarding the developing roller, Japanese Patent Laid-Open No. 6-130792 proposes a developing roller employing a method in which portions that have different electric resistances or dielectric constants are exposed and mixed on a front surface thereof at a regular and fixed pattern pitch, and in which a number of micro electric fields are formed on the front surface thereof. By employing the above method, an appropriate amount of toner can be adhered to the electrostatic latent image on the photosensitive drum; accordingly, an image that has high image density and that has an excellent diagram reproducibility and gradation can be obtained.
Note that in the developing roller described above in which portions with different dielectric constants are provided on the front surface, there are cases in which the electric resistance of the dielectric unit dependent on the environment changes depending on the material of the dielectric unit such that the toner adhesion amount on the developing roller changes according to the environment in which the developing roller is used. In order to overcome such a problem, Japanese Patent Laid-Open No. 4-31880 discloses a technique in which a material having a smaller variation difference in the volume resistivity of the dielectric unit is used.
However, with the method using a supply roller, since, other than the developer carrying member (a developing roller), a mechanism for rotating the supply roller is needed and, furthermore, since there is a limit to the extent to which the supply roller can be miniaturized, it is difficult to achieve miniaturization and simplification of the overall developing apparatus.
On the other hand, with the method that does not use a supply roller, while the above problem is alleviated, it will be difficult to supply the developer to the developer carrying member in a stable manner.
In other words, when the pressure of the developer against the front surface of the developer carrying member is insufficient, cases in which the developer required to form an image not being sufficiently carried onto the developer carrying member occur.
On the other hand, if the pressure of the developer against the developer carrying member is too high, aggregated developer becomes easily formed in the vicinity of the developer carrying member. Since the aggregated developer hinders the developer from being supplied to the developer carrying member, there are cases in which the developer is not sufficiently carried onto the developer carrying member.
Furthermore, in the case of the apparatus configuration that does not use the supply roller, the electric resistances of the dielectric units on the front surface of the developing roller disadvantageously changes according to the environment in which the developing roller is used such that, disadvantageously, the toner coat amount on the developing roller changes according to the environment. It is considered to be one of the effective techniques to use a material that has, in the volume resistivity of the dielectric unit, a small variation difference in order to overcome the above problem.
However, the technique of suppressing the resistance variation of the dielectric through the material that is used limits the material that can be used. There are cases in which it is difficult to make the developing roller, which is capable of being mass manufactured inexpensively, to have a desired characteristic; accordingly, a limit is met in the application thereof when balancing with mass productivity.